The present disclosure relates generally to electronic circuits, and more particularly to a method and an apparatus for improving the performance of amplifiers.
In analog or mixed circuit design, it is desirable for amplifiers to have a high gain, large bandwidth, high input impedance, low output impedance, and linear performance. It is well known that amplifiers having transistors coupled in a cascode topology (typically include telescopic cascode and folded cascode configurations) provide higher effective load resistance, reduce voltage-induced nonlinearities, and reduce Miller effect (caused by coupling between the output and the input). The folded cascode amplifier topology may be used to improve output range compared to the telescopic cascode. It is desirable that transistors used in the folded cascode amplifier operate in the saturation region to provide constant current. However, changes in the input(s) to the folded cascode amplifier may cause the folded cascode amplifier to operate in an overload condition. That is, changes in the input voltage of the folded cascode amplifier which exceed a threshold value may cause the output of the folded cascode amplifier to swing in an uncontrolled manner to a high or low voltage supply level during the overload. The overloading on the folded cascode amplifier reduces the effectiveness of the cascode current mirrors.
Upon removing the stimulus causing the overload, a recovery of the folded cascode amplifier from the overload condition includes restoring the transistors to operate in the saturation region. However, due to the presence of parasitic capacitance of the transistors or use of a compensation capacitor, performance of the folded cascode amplifier while recovering from the overload condition may become too slow for some applications such as high speed analog or mixed signal circuits. Therefore, a need exists to provide an improved folded cascode amplifier that is capable of recovering quickly from an overload condition.